The invention relates to an inherently short-circuit resistant power supply system, by which electronic assemblies disposed in a decentralized manner can be supplied.
The power distribution system is particularly suitable for supplying electronic assemblies for deep ocean oil production, that is to say for supplying electronic assemblies which are located on the seabed. The following text therefore refers to this application, although the power distribution system is generally applicable.
In deep ocean oil production, many of the processes to be controlled cannot be disposed centrally at one point. Some of the electrical equipment is located on the drilling island, while more of it must be disposed in pressure-resistant containers in the vicinity of the bore holes on the seabed, in which case the distance between the drilling island and the electrical equipment on the seabed is in some cases more than 1 km.
Power is in this case normally supplied to the electrical equipment (sensors, small motors, etc.) on the seabed centrally via a long underwater cable with an AC voltage at a low frequency (50 to 60 Hz) from the drilling pylon. On the seabed the power is then once again distributed using cables with the aid of a transformer, in a star shape to the, in generalized form, n endpoints (bore holes). The voltage at the n endpoints is stabilized by suitable power supply units. Various loads (sensors, small motors etc.) are connected to the outputs of the power supply units.
A distributed power supply system for installations such as these must be very robust and reliable since it is virtually impossible to replace the system on the seabed, or this can be done only with a very high cost penalty. The n outputs of the system must in this case individually be resistant to short circuits, and a short circuit (for example as a result of rocks striking the connecting cable to the power supply unit) must never lead to failure of another output. Therefore, even in the event of a short circuit of m connecting cables (mxe2x89xa6nxe2x88x921), the serviceability of the remaining output must not be adversely affected. A partial short circuit is also conceivable if, for example, a rock cuts through the insulation of the current-carrying conductor and thus causes a considerable current flow through the conductive seawater surrounding the cable. In a case such as this, a current can occur overall in the supply cable and in the distribution transformer which, although it does not lead to tripping of a protection device on the drilling island (for example being two or three times the rated current) it can, however, actually lead to permanent damage due to overheating of the power distribution system on the seabed.
By way of example, the number of end points is chosen to be n=4 in the following text, in order to describe the power distribution system. This is done not only to explain the prior art, but also, subsequently, to describe the invention.
If the power levels to be transmitted are small (for example  less than 10 W per output), then the short-circuit resistance is normally ensured by bimetallic switches which are disposed in series with the cables and are connected directly to the connection on the secondary side of the transformer, open in the event of a short-circuit current and then always switch on and off again with the specific time constant for the bimetallic switch. For higher power levels (for example 1 kW per output), this method for ensuring short-circuit resistance is no longer feasible. In consequence, other circuitry or measures are required in order to ensure short-circuit resistance.
It is accordingly an object of the invention to provide an inherently short-circuit resistant power distribution system which overcomes the above-mentioned disadvantages of the prior art devices of this general type, which satisfies the requirements for short-circuit resistance with a high level of efficiency and, furthermore, with low production costs.
With the foregoing and other objects in view there is provided, in accordance with the invention, a power distribution system for supplying power to electronic assemblies. The power distribution system contains a distribution transformer having a core and windings disposed on the core. The windings including a primary winding and a number of secondary windings, and the windings on the core are subdivided into a number n of winding packs corresponding to the number of the secondary windings. Each of the winding packs has an n-th (1/n) part of the primary winding and one of the secondary windings. A supply cable is connected to the primary winding. A voltage source is connected to the supply cable and supplies electrical power through the supply cable to the primary winding. Connecting cables are provided and each connects one of the electronic assemblies to one of the secondary windings.
One particularly advantageous configuration is to use a distribution transformer with four secondary windings, since a U-shaped core can then be used and a uniformly distributed winding configuration is possible in a simple manner.
In accordance with an added feature of the invention, a further transformer is provided and the voltage source is connected to the supply cable with an interposition of the further transformer.
In accordance with another feature of the invention, the connecting cables and the supply cable are deep ocean cables.
In accordance with an additional feature of the invention, power supply units are provided and the electronic assemblies are each connected to one of the connecting cables with an interposition of one of the power supply units. Each of the power supply units are set up to supply a stabilized DC output voltage from an AC input voltage which changes in a ratio of 1:n.
In accordance with a concomitant feature of the invention, the number n is equal to 4, and the core is a UU-shaped core having four core limbs each fitted with one of the winding packs.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an inherently short-circuit resistant power distribution system, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.